Intel's X25-E SSD runs circles around rivals

There's something special about installing what is arguably one of the fastest, most sophisticated solid-state disk (SSD) drives in your average Dell laptop. It's a little like stuffing a big-block V8 into a Chevy Chevette -- you get amazing performance, but no matter how hard you try, you can't justify the cash you just shelled out in order to go really fast.

Intel Corp.'s X25-E Extreme SATA SSD (model SSDSA2SH064G1GC) is an enterprise-class drive meant for use in data centers, not run-of-the-mill laptops. But the drive has become one of the better known SSDs because Intel was early to the market with it and because of its sophisticated architecture, screaming performance and stalwart reliability.

My goal was to see if that reputation is deserved, especially given the interest in all things SSD among early technology adopters.

For my tests, I used a Dell Latitude D830 with a 2.4-GHz Intel Core 2 Duo processor running Windows XP Professional SP2. I wanted to test the drive to see how its use would affect the laptop's battery life, so I used MobileMark 2007, a BAPCo benchmark application that simulates the typical use of common applications such as PowerPoint, Outlook and Excel. For I/O performance tests, I used both ATTO Technology's ATTO Disk Benchmark v2.34 and Simpli Software's HD Tach v3.0.4 benchmarking utilities.

The guts

Unlike Intel's consumer SSD, the X25-M, the X25-E is built with single-level cell (SLC) NAND flash chips, which store one bit per cell, unlike multilevel cell (MLC) flash, which stores two or more bits per cell. While MLC flash offers greater capacity natively, SLC delivers better performance, reliability and longevity. But it also costs: A 64GB X25-E goes for more than US$800 ($1,001 AUD) on Pricegrabber.com. In comparison, Intel's 80GB X25-M will run you around $360.

But if you need unerring reliability and longevity, an SLC drive is the one you want. It has a more sophisticated controller and can handle about 100,000 write/erase cycles -- about 10 times the number of cycles the best MLC-based drives on the market can handle.

The X25-E gets its native speed from the SLC memory and from the fact that it interleaves NAND flash chips and uses 10 parallel channels to those chips. Intel is not alone in the use of a multichannel architecture, but it was among the very first to hit the market with it. The X25-E also relies on a proprietary controller with firmware that performs native command queuing and advanced wear-leveling and write amplification reduction operations.

Wear-leveling and write amplification algorithms are common in today's midrange and enterprise-class SSDs. Wear-leveling algorithms are used to more evenly distribute data across flash memory so that no single section wears out faster than any other, prolonging the life of whole drive. The controller in wear-leveling operations keeps a record of where data is set down on the drive as it's relocated from one portion to another.

Write amplification refers to an issue common to all SSDs. When any portion of the data on the drive is changed, a block must first be marked for deletion in preparation for accommodating the new data. For example, a read-modify-write algorithm in an SSD controller will take a block that's about to be written to, retrieve any data already in it, mark the block for deletion, redistribute the old data, then lay down the new data in the old block.

The amount of space required for each new write can vary, but according to Knut Grimsrud, a director of storage architecture in Intel's research and development laboratory, the write amplification factor on many consumer SSDs is anywhere from 15 to 20, meaning that for every 1KB of data written, 15KB to 20KB of capacity is actually used. Intel claims that the X25-E Extreme's write amplification factor is less than 1.1, so it performs write operations more efficiently than most other SSDs.

The 64GB model of the X25-E actually has 80GB of raw NAND flash capacity. It uses the difference for provisioning to get to 64GB. The drive also uses 256KB worth of cache to improve write performance.

Because the drive uses more reliable and sustainable SLC flash memory, it has a mean time between failures (MTBF), or life expectancy, of about 2 million hours. The X25-M's MTBF is 1.2 million hours (Note: MTBF is not a reliable way of measuring SSD longevity, but it's commonly used by vendors for comparison purposes.)

The X25-E looks exactly like the X25-M; it comes in an austere black enclosure, adorned only with a simple white manufacturer's specification label. (Yes, some vendors actually do try to gussy up their internal drives with stainless steel and colorful stickers). The drive comes in 32GB and 64GB capacities; I tested the larger 64GB model.

Performance tests

Intel's specifications say the drive offers a sustained sequential read rate of up to 250MB/sec. and a sustained sequential write rate of up to 170MB/sec., but performance depends on use. Small, random operations are less efficient than long sequential reads and writes. Average PC users tend toward random operations when using common applications like e-mail or surfing online.

The drive can produce up to 35,000 4KB random I/O per second (IOPS) and 3,300 4KB random write IOPS. In NAND flash memory, blocks consist of a number of pages and each page is either 512, 2,048 or 4,096 bytes in size. Therefore, a 4KB block more efficiently fills the memory.

Troy Winslow, marketing manager for the NAND Products Group at Intel Corp., said, "We've even done studies showing 80% of all OS requests are in the 4K-to-16K range, yet many SSDs were designed on older controller technology that was requesting large file-size transactions of 128K in size. All SSDs perform best at the smaller file size."

The X25-E consumes 2.6 watts of power when active and 0.06 watts when idle.

Using the ATTO benchmark, the drive turned in a 252MB/sec. sequential read rate and a very impressive 208.8MB/sec. sequential write rate. Using HD Tach, the drive showed a 200.3MB/sec. average write rate with 240.6MB/sec. burst (or peak) data transfer rate. The HD Tach software also revealed a random data access rate of 0.1 milliseconds and an 8% CPU utilization rate.

In comparison, with the OCZ Technology Corp. midrange Vertex SSD drive I recently reviewed, the ATTO benchmark software showed a read rate of 244MB/sec. and a write rate of 172MB/sec. The Vertex uses cache -- 64MB worth -- to increase write rates, and it has a multichannel architecture. But it couldn't beat the X25-E's SLC flash memory. It did beat it on price, however. The 128GB OCZ drive goes for less than $400.

Next, I copied a 1GB file containing photos and videos in a desktop folder to the SSD. The copying took 13 seconds.

The X25-E blows away any other drive I've tested when it comes to OS boot times. The Dell needed just 15 seconds to boot Windows, and 20 seconds to do so with a restart. (The OCZ Vertex was a little slower, booting the machine in 20 seconds and restarting in 26 seconds.)

I've tested enough SSD drives in recent months to become convinced that the drives have little effect on laptop battery life for better or worse. Each time I test an SSD against a hard disk drive, I see no more than a difference of about five minutes in battery life.

That's also true for Intel's X25-E. The BAPCo software indicated a battery life rating of 136 minutes when using the X25-E. The battery life on the same computer using a Seagate Momentus 7200.4 500GB hard disk drive was rated at 132 minutes. As a follow-up to that, I also fell back on the old DVD movie test. The battery was depleted after 135 minutes using the X25-E.

Conclusion

While few people would shell out big bucks for a laptop drive, it's always important to keep an eye on the top of the technology heap. Other SSD drives may not hit the speeds of the X25-E, but the technology shows what SSDs could be delivering down the road. Intel remains the industry leader, though other companies are hoping to encroach on its territory.

Again, like STEC Inc.'s flagship Zeus or Micron Technology Inc.'s RealSSD P200 SSD drives, Intel's X25-E is positioned for the data center, where it can replace multiple, 15,000-rpm Fibre Channel drives to offer storage administrators better performance and capacity. That said, if you've got money to burn and love the thought of having the best performing and most reliable laptop drive holding your data, Intel's top-of-the-line SSD will aptly fill the bill.

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